This invention relates generally to processes for forming paperboard products and to the products formed by such processes. More particularly, this invention relates to a method of making disposable paperboard containers with textured coatings and to the texture-coated containers formed by that method. This invention also relates to coatings having superior bulk and insulation properties.
This invention relates to paperboards on which are printed insulating and/or textured coatings having a high coefficient of friction. The static coefficient friction of the paperbound has values of about 0.2 to 2.0 and above, preferably 0.3 to 1.0 and the kinetic coefficient of friction is about 0.22 to 2 suitably 2 to 1.5 and preferably 0.22 to 0.85. These values are shown in FIGS. 9A and 9B and are up to five times greater than the corresponding coefficient of friction values of conventional paper plates, plastic plates and foamed plates. The printing of the coating is an efficient, precise process and allows that only at least ten percent of the container surface has to be coated to achieve the beneficial insulation and handling properties. These containers are particularly suitable for use as hot drink containers since only a small portion of the outer surface of the container has to be printed. Competing foamed polyolefin insulated coating cannot be printed on the surface of the paperboard and consequently the whole side of the paperboard has to be coated. Thus, the coated containers of this invention having superior insulation and bulk properties, have greater inherent cost advantages over the prior art foamed polyolefin extrusion coated containers. Furthermore, registered texture coated containers exhibit excellent printing clarity and accuracy which cannot be obtained when coatings are prepared from foamed polyolefins.
Disposable paper containers, such as plates, trays, bowls, airline meal containers and cafeteria containers, are commonly produced by pressing flat paperboard blanks into the desired shape between appropriately shaped and heated forming dies. Various protective coatings are typically applied to the blanks before forming to make the resulting paperboard containers moisture-resistant, grease-resistant, more readily printable, etc. Often, printing is also applied to the top surface for decoration. A large number of paper products are produced by this method every year. These products come in many different shapes and sizes, including round, rectangular and polygonal. Many such containers, including for example airline meal containers, have a number of independent compartments separated by upstanding ridges formed in the inner areas of the containers.
When a container is made by pressing a flat paperboard blank, the blank must contain enough moisture to make the cellulosic fibers in the blank sufficiently plastic to permit it to be formed into the desired three-dimensional container shape. During the pressing operation, most of this moisture escapes from the uncoated bottom surface of the blank as water vapor. Suitable methods of producing paperboard containers from moistened paperboard blanks are generally described in U.S. Pat. Nos. 4,721,499 and 4,721,500, among others.
Many people prefer disposable containers which, when handled, produce a sense of bulkiness and grippability at least suggestive of the more substantial non-disposable containers which they replace. While a sense of bulkiness may be provided to some extent in styrofoam and thick pulp-molded containers, such containers suffer a number of drawbacks. For example, unlike pressed paperboard containers, styrofoam containers are often brittle and they are environmentally unfriendly because they are not biodegradable. Also, styrofoam containers are not cut-resistant and it is difficult to apply printing to the surface of styrofoam containers. Additionally, because of their bulkiness, styrofoam containers take up large amounts of shelf space and are costly to ship. Pulp-molded containers similarly are not cut-resistant and have poor printability characteristics. Additionally, pulp-molded containers typically have weak bottoms. Pressed paperboard containers, however, are cut-resistant, readily printable, strong in all areas, and are far less bulky than styrofoam or pulp-molded containers.
The present invention thus is an improvement in pressed paperboard containers. In the present invention, environmentally friendly disposable paperboard containers are formed. By printing the insulating textured coating on at least ten percent of one surface of the paperboard, the insulating and/or textured containers were formed which give users handling them a sense of bulkiness and grippability. These new containers rely on efficient processes of press-forming paperboard blanks. The resulting product, which consists primarily of cellulosic material, is nearly entirely biodegradable. Additionally, it will withstand normal microwave conditions without any significant change in caliper, it has substantially better thermal resistance when compared to prior disposable paperboard containers made without such an insulating and/or textured coating, and it tends to stay put when resting on a smooth surface due to the coefficient of friction of the textured coating. It should be noted that prior art polyolefin foamed coatings cannot be pattern applied and therefore have to cover the whole side of the board.
The data shown in FIGS. 9A and 9B deomonstrates that conventioinal paper plates have a coefficient of kinetic friction of about 0.18, plastic plates have a coefficient of kinetic friction of about 0.2 and foam plates have a kinetic coefficient of friction of slightly under 0.2. The coefficient of kinetic friction of the textured plates of this invention have values of about 0.61 to 1.4 up to 2.0 and more. Thus, the coefficient of kinetic friction of our texturized plates of this invention are about three to four times greater than for our conventional paper plates. Suitable coefficient of kinetic friction for our texturized containers is about 0.22 to about 1.5 advantageously 0.4 to 0.8 preferrably 0.5 to 7.
The data shown in FIGS. 9A and 9B deomonstrate that conventional paper plates have a static coefficient of friction of 0.19, for plastic plates it is the same and for foam plates the static coefficient of friction is 0.2. The static coefficient of friction of the textured plates and containers of this invention have a static coefficient of friction of 0.22 to 2.0 and above, the preferred values are 0.8 to 1.6.
The texture coated cellulosic paperboard must reconcile several conflicting properties to be useful for the manufacture of plates, cups, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, and related articles of manufacture. The coated paperboard has to have improved thermal resistance, improved formability, and, to be economical, the whole board should not be covered with the coating. All the conventional paperboards can be utilized; but for enhanced insulation properties, the fiber weight (hereinafter xe2x80x9cwxe2x80x9d) of the paperboard should be at least about forty pounds for each three thousand square foot ream. Fiber weight is the weight of fiber in pounds for each three thousand square foot ream. The fiber weight is measured at standard TAPPI conditions which provide that the measurements take place at a fifty percent relative humidity at seventy degrees Fahrenheit. In general, the fiber weight of a 3000 square foot ream is equal to the basis weight of such a ream minus the weight of any coating and/or size press. The fiber mat density of the paperboard utilized in the manufacture of textured containers is in the range of about 3 to 9 pounds per 3000 square foot ream at a thickness of 0.001 inch. The preferred fiber mat density is in the range of about 4.5 to 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. To achieve the superior properties of textured paperboard containers, it has been discovered that the board at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a thickness of 0.001 inch, should have a GM Taber stiffness of at least 0.00716 w2.63 grams-centimeter/fiber mat density1.63, and a GM tensile stiffness of at least about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness value for paperboards having the fiber mat density given above is 0.00501 w2.63 grams-centimeter/fiber mat density1.63, and the GM tensile stiffness is 1323+24.2 w pounds per inch. The high GM Taber stiffness values listed are desired to facilitate the bending of the paperboard into the aforementioned articles of manufacture and to provide these articles with greater rigidity. Likewise the high GM Taber and GM tensile stiffness prevents the plates, cups, and other articles of manufacture from collapsing when used by the consumer. The articles of manufacture can suitably be prepared from either one-ply or multi-ply paperboard as disclosed herein. Suitable one-ply and multi-ply paperboards comprise (a) predominantly cellulosic fibers, (b) bulk and porosity enhancing additive interspersed with the cellulosic fibers in a controlled distribution throughout the thickness of the paperboard, and (c) size press applied binder coating optionally including a pigment adjacent both surfaces of the paperboard and penetrating into the board to a controlled extent. The amount of size press applied is at least one pound for each three thousand square foot ream of paperboard having a fiber mat density of about 3 to below 9 pounds per 3000 square foot ream at a board thickness of 0.001 inches. For boards having a fiber mat density of 9 or greater per 3000 square foot ream at a board thickness of 0.001 inch, the amount of size press applied should be at least six pounds for each three thousand square foot ream. The overall fiber weight of the paperboard is at least 40 lbs. per 3000 square foot ream, suitably 60 to 320 lbs. per 3000 square foot ream, preferably 70 to 240 lbs. per 3000 square foot ream, most preferably 80 to 220 lbs. per 3000 square foot ream, and the distribution of the bulk and porosity enhancing additive is controlled so that at least twenty percent of the additive is distributed in the central layer and not more than 75 percent of the additive is distributed on the periphery of the paperboard with no periphery having more than twice the percent of the additive distributed in the central layer of the paperboard. The penetration of the size press applied binder and optionally pigment coating into board is controlled to produce a cellulosic fiber board web having at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a thickness of 0.001 inch, a GM Taber stiffness respectively of at least 0.00716 w2.63 grams-centimeter/fiber mat density1.63, and GM tensile stiffness of about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness for the paperboard for the bulk enhanced fiberboard having a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a board thickness of 0.001 inch is 0.00501 w2.63 grams-centimeter/fiber mat density1.63, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. The GM tensile and GM Taber values for the web and one-ply board are the same. For multi-ply board the overall paperboard GM Taber stiffness and GM tensile stiffness are the same as for a one-ply paperboard. The aforementioned combination of GM Taber stiffness and GM tensile stiffness provides a paperboard which can readily be converted to useful high quality textured or insulation coated cups, plates, compartmented plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, and other consumer products and other useful articles of manufacture which have the outer surface partially texture coated and/or insulation coated.
The texture coated and/or insulation coated disposable paperboard containers of the present invention are formed from flat paperboard blanks having two surfaces by: 1) printing on one surface of the blank with a textured or insulating coating covering at least ten percent of the surface, suitably ten to ninety-five percent of the surface, and preferably twenty to) sixty, percent of the surface; the textured or insulating coating comprises a liquid polymeric binder mixed with either (a) microspheres, (b) gases, (c) glass beads, (d) hollow glass beads, and (e) a mixture of these wherein said binder, after being mixed with the aforementioned components, expands and cures when appropriately heated; 2) optionally coating the other surface of the blank with conventional grease-resistant, decorative and other coatings; 3) applying heat to expand and cure the surface printed with the textured and/or insulation coating; 4) optionally adding moisture to the two coated blanks; and 5) optionally applying heat and pressure to make a texture and/or insulation coated container. For superior insulation properties, solid glass beads are suitably replaced with hollow glass beads.
The data shown in FIGS. 9A and 9B demonstrate that conventional paper plates have a coefficient of kinetic friction of about 0.18, plastic plates have a coefficient of kinetic friction of about 0.2 and foam plates have a kinetic friction of slightly under 0.2. The coefficient of kinetic friction of the textured plates of this invention have values of about 0.61 to 1.4 and above. Thus, the coefficient of kinetic friction of our texturized containers including plates is about three to seven times greater than prior art paper plates. Suitable coefficient of kinetic friction for our texturized container is about 22 to about 2.0 and above 0.4 to 0.9 preferrably 0.5to 0.7.
The data shown in FIGS. 9A and 9B demonstrate that conventional paper plates have a static coefficient of friction of 0.18. The static coefficient of friction of the textured plates and containers of this invention have a static coefficient of friction of 0.2 to 2.0 and above suitably 0.4 to 1.5 preferably 0.4 to 1.0. The static coefficient of friction of our plates and containers is about two to ten times greater than for conventional paper plates.
The liquid coating suitable for printing comprises a liquid polymeric binder mixed with one of the following: (a) gases, (b) microspheres, (c) glass beads, (d) hollow glass beads and (e) a mixture of these. The heat hardenable polymeric binder is liquid when applied to the paperboard blank. Any polymeric binder which is liquid at the application temperature and is compatible with the microspheres, gases, glass beads, hollow glass beads, or a mixture of these, and which cures as a result of heating can be used. Generally, in its cured state, the polymeric binder must adhere tightly to the substrate and it should not be unduly brittle, since brittle coatings tend to flake and pull away from the paperboard substrate. In a preferred embodiment, the polymeric binder will not harden until expansion of the microspheres or gases is substantially complete.
Examples of thermoplastic polymers, which may be used as binders include polymers of ethylenically unsaturated monomers, such as polyethylene, polypropylene, polybutenes, polystyrene, poly (a-methyl styrene), polyvinyl chloride, polyvinyl acetate, polymethyl methacrylate, polyethyl acrylate, polyacrylonitrile and the like; copolymers of ethylenically unsaturated monomers such as copolymers of ethylene and propylene, ethylene and styrene, and polyvinyl acetate, styrene and maleic anhydride, styrene and methyl methacrylate, styrene and ethyl acrylate, styrene and acrylonitrile, methyl methacrylate and ethyl acrylate, methyl methacrylate and acrylonitrile and the like; polymers and copolymers of conjugated dienes such as polybutadiene, polyisoprene, polychloroprene, styrene butadiene rubber, ethylene-propylene-diene rubber, acrylonitrile-styrene butadiene rubber and the like; saturated and unsaturated polyesters including alkyds and other polyesters; nylons and other polyamides; polycarbonates; polyethers; polyurethanes; epoxies; ureaformaldehydes, phenol-formaldehydes and the like.
In addition, such polymers can be formulated with curing or cross-linking agents which activate at microsphere or gas expansion temperatures to provide foamed, cured or cross-linked variations of the foregoing types of polymers. Such curing and cross-linking techniques are well-known in the art and include for example, the use of free radical generators such as peroxides and the like, compounds reactive with double bonds such as sulfur and the like, or compounds reactive with pendant groups of the polymer chain such as the reaction products of polyisocyanates with pendant hydroxyl groups, the reaction products of polyols with pendant isocyanate groups and the like.
One particularly preferred resin is Acronal S504, which is a styrene acrylic derivate (latex) manufactured by BASF Corporation of Parsippanny, N.J. having a solids level of about 50% by weight and a glass transition temperature of about 4 and containing, in mole percent:
Airflex 456 is also suitable. It is a terpolymer emulsion of vinylchloride, ethylene and vinyl acetate having a glass transition temperature of about 0xc2x0 to 3xc2x0 C.
The coating formulation may also include a mineral filler to increase the solids level of the microsphere/polymericbinder or gas/polymeric binder mixture. The mineral filler should be present at a level of about 0 to 50 percent by weight and more preferably about 20 to 40 percent by weight. Suitable mineral fillers include, for example, kaolin clays, calcium carbonate, titanium dioxide, zinc oxide, chalk, barite, silica, talc, bentonite, glass powder, alumina, graphite, carbon black, zinc sulfide, alumina silica, and mixtures thereof. Hydrafine clay, which is a hydrated aluminum silicate or koalin with 0.9-2.5% titanium dioxide manufactured by J.M. Huber Corp. of Macon, Ga. is a preferred mineral filler.
Microspheres are suitable for coating our paperboard and containers; however, part or all of the microspheres can suitably be replaced with a gas, solid glass beads, or hollow glass beads. Suitable gases include: air, nitrogen, helium, isobutane, and other C1 to C7 hydrocarbons and etc.
The texturizing agent or insulation agent/polymeric binder mixture should be applied by printing in a generally uniform pattern covering at least about 10% and no more than about 95% of one surface area of the paperboard blank. Preferably, coverage will be about 30-50% of one surface area. The textured and/or insulating coating, after heating and curing, should exhibit a caliper ranging from about 0.001 to 0.015 inch and preferably from about 0.005 to 0.010 inch.